However, his political viewpoint was changed during the Great Depression in the 1930s. Seeing the plight of workers in that situation (including himself), he became politically radicalized to the left.

Dobbs served as mentor and advisor to a young Jimmy Hoffa, while Hoffa was making his rise within the Teamsters, eventually becoming its president in 1957. Dobbs primarily inspired Hoffa with his view that the capitalist system was a Darwinian struggle, where power, rather than morality, was the primary factor determining the eventual outcome.[2]

For opposing World War II, he and other leaders of the SWP and the Minneapolis Teamsters were convicted of violating the Smith Act, which made it illegal to "conspire to advocate the violent overthrow of the United States Government." He served over a year in Federal Correctional Institution, Sandstone, from 1944 to 1945.

Farrell Dobbs retired in 1972, but remained in the party until his death in 1983. He devoted the later part of his life to historical documentation of the American leftist movement and the Minnesota Teamsters. Dobbs was the author of a four-volume history / memoir of the Minneapolis struggles: Teamster Rebellion, Teamster Power, Teamster Politics and Teamster Bureaucracy. He had completed two volumes of a planned history of the Marxist movement in the United States at the time of his death, titled: Revolutionary Continuity: The Early Years, 1848-1917 and Birth of the Communist Movement, 1918-1922.